Potential indicator



Nov. 28', 1944.

Filed Oct. 12, 1943 4 4 o a 3 a z I Z I I m m j S #m fi 1 --L. y H ,5. M m A+ I T 7. Pu E r A at o .M a w Z 3 I 4 f M W F! n 7 1 tively light weight.

Patented Nov. 28, 1944 Application cto ber 'lf i, 19413,, Ser ialNo. 505,995? e i This invention has to dowith instruments for indicating and/ or testing potentials. A potential indicator of small bulk and simple structure is j desirable for purposes of voltage testing in situations where no great accuracy is necessary. Such an instrument should be capable of use on either alternating or direct current lines and shouldbe capable of indicating. awiderange of voltages.

- Attempts have been made in the past tosupply aninstrumentof. the character noted, but they have been deficient in one ormoreof the qualities desirable in such an instrument. Those qualities are, generally speaking, maximum simplicity in design, low cost of manufacture, reliability in i use, and ruggedness against being thrown out of order or otherwise injured due to accidents, misuse or abuse. Thesequalities, coupledwith minimumweight. and ,bulk are the general ob- 3 jectives whichmy inventio-n'reaches, and those 1 objects and the manners in which they and others are reached, will best appear from the following detailed description. of preferred structures 11-.

lustrative of the invention, shown in the accompanying drawing in which: i i

Fig. 1 is a vertical longitudinal-section of one form of my instrument; h

Fig. 2 is a section takenas indicated by line 2---2 on Fig. 1, with certain partsshown in elevation;

Fig. 3 is afragmentary side elevation taken as H indicated by line 3-3 on Fig.1;

Fig. 4 is a cross section on line,4-4 of Fig.

1; and

Fig. 5 is a section similar to that of Fig. 2 but showing. a somewhat modified structure.

In the drawingthe instrument is shown as housed in a cylindric casing l0, one end of which i may be closed by an end wall ll which may be formed integrally with the cylindric wall. Casing end ll may, as will be obvious, be either in the form of a removable cap or plug; but I prefer to form it integrally with the cylindric side Wall.

The casing, as well as certain interior parts of the instrument may be made of anysuitable material,

but preferably of some insulating material, and

whole I may term themounting core ofthe instrument.

This mounting ,core; indicated generally by the numeral |5,is madeup principally of a central sleeve l6 with upper and lower heads H and 18 at its ends,. and of .two spaced exten sions. l9 which project upwardlyfrom upper head l1 to the upper or closed end of the casing All of these major partsof the mounting core are unitary and preferably made in one integral'piece and preferably, as. notedabova of some molded material such as a plasti c. w'I he central sleeve l6 and the two heads 11 and. Norm thespool for either the single coil 2ll shown in Figs. 1 and 2 or themultiple coils a, 201), shown; in Fig. 5. Thelowerhead; I8 hasan upper flangedportion la 1 it which directly forms the winding spool head; then immediately below flange 18a it has" an annularly recessed or reduced portion 18b which provides spacebetween it and cylindricwall l0 for the wire connections, and then below portion [8b it has an .enlarged flanged head portion l8cywhich fits the otherwise open end of easing; ID to act asa .IA registration pin 10,

closure for that end. mounted in head I80, fits into a notch lll in case It, to register themountingcore in its proper position so that pointer 32: willregister with casing yslot-45 when theparts are assembled. i

When the described mounting core is inserted a in the casing, its length is such that--when the closure head I 80 engages the open end of the casing, the upper ends of extensions H? are substantially in contact' with or closeto the upper preferably also of some material which is of low density sothat the whole instrument is. of rela- For instance the external casing maybe of some fibrous material and the major portion of the interior structure, to be de- 1 scribed, may be of wood. .-Itis preferred however to form all such plastic. i i i Within the casing, fitting it snugly but with easy removability, there is a member "which as a and islooped, at is upperend at 3!, through a hole ina light thin pointer 32. Pointer 32Iis parts of somesuitable molded preferably thin anddlat. as illustrated and is made casing head. ll. A pair of screws such as indicated at 2! pass through head] I and thread into openingsin extensions 19 to holdthe mounting corein place. U i

. Spool sleeve l6 has a longitudinal bore which extends through ;it and thetwo, heads I] and 18. This bore accommodates a small solenoid core 26 whose normal position is in the upper end of the bore as shown inFig. 1., The bore also accommodatesi a light coiled spring 21. under core 26 and resting at itsjlower endupon an adjustment screwfl28 which is threaded into the lower end of bore 25. By adjusting screw 28 and settingitwith the lock nut. 29, the position of spring 21 with relation to armature core 26 maybe adjustedand set. i M i 1 i A small connecting rod or wire 30 extends up-.

wardly from the upper'end of armature core 26 preferably of some light thin sheet metal. Itis mounted atiits pivoted end ona pivot spindle 33 which extends transversely across the space between the two upper extensions I9 and is pivotally supported between those two extensions. For instance one of the extensions l9 may have a countersunk pivot bore or depression 34 in its inner face, andthe other extension l3 may be provided withan adjustable pivot screw 35 which has a so formed and so attached that its spring tension will substantially just support the weight of core 26, wire 30, and pointer 32 in the relative normal position shown in Fig. 1 with core 26 at the upper end of bore and with the outer end of pointer 32 at the upper end of casing slot and preferably exerting a slight pressure upwardly against the end of the slot. Core 26 although of iron or some similar magnetic permeable material, is quite light; The drawings show the whole instrument in an actual size which is practical. Pointer 32 is also very light, being quite thin (its thickness is somewhat exaggerated in the drawing) and it also can be made of some light metal such as aluminum or an alloy. Hair spring 40 need not be very strong in order to support the weight of the mentioned parts; and if the hair spring supports the parts so that the outer end of pointer 32 presses upwardly with a slight pressure against the upper' end of slot 35, a fairly considerable jar or blow on the instrument will not move the pointer downwardly even though the hair spring is quite delicate and the movement of the parts under electromagnetic forces is also quite delicate. The pointer plays in the vertical casing slot 45, moving downwardly in the slot to or toward its lower end. In its uppermost normal position the end of the pointer is preferably completely recessed in the slot where it is not liable to be accidentally engaged by any external object which might force it or injure it. These arrangements and proportionings of the parts provide an instrument which is quite delicate in its operations, but at the same time is quite fully proof against injury when the instrument is loosely carried in a pocket or even when it is subjected to accidents or abuse. And the pointer 32, besidesbeing in a protected position normally, is also of such length that in its downward swinging motion it projects little, if

any, outward beyond the defining edges of slot 45.

'Hair spring '40 is, as mentioned above, quite delicate. In practice it is formed into a coil of about the proportions and dimensions shown in the drawings and is made of steel spring wire 0.009 inch diameter. When the instrument is in use the current which flows through coil 20 sets up a magneto-motive force which increases for higher voltages and thus tends to draw core 26 further downwardly against the tension of hair spring 40. The tension of the delicate hair spring 40 does not increase very fast as pointer 32 is moved downwardly. In order to provide an instrument which is capable of being used over a wide range of voltages within a reasonably short movement of the pointer, and at the same time to provide for the delicacy of pointer movement which is essential to accurate indications of the lower voltages, I employ in combination with the delicate hair spring the reenforcing spring-'21 below core 26. This reenforcing spring, although also relatively light, is stronger in spring tension than the hair spring. To give an illustration of a desirable spring strength in the specific instrument which I am describing here, I may say that spring 21 is about in diameter, three-quarters pointer 32 under different potentials corresponds to the A. C. and D. C. indications which are shown in Fig. 3 on the outside of the case alongside the opposite edges of slot 45. The approximate range of potentials which the specifically described instrument will indicate and measure is illustrated by the range of the scale figures.

For an instrument of the size and proportions and voltage ranges shown, coil 20 is for instance wound with No. 40 enameled copper wire, total coil resistance (D. C.) being about 3000 ohms. The ends of the coil winding come out, as is shown for one of the ends in Fig. 2,. at and are se cured to contact strips 5| which in turn are se cured to the recessed head portion I812 by binding screws 52. Binding screws 52 also secure the ends 53 of the two flexible lead-in wires 54,.the wires passing through head-portions 13c and l8b through bores which are indicated (one of them) at l8d-. Externally of the instrument case the flexible cords 54 may be suitably supported and protected against breakage at their entrance to the bores by any suitable'or known means, unnecessary to illustrate here. The cords may be of any suitable length and equipped at their ends with any suitable contact pieces and insulating handles.

Fig. 5 shows a slight modification which may Coil 20 of Fig. 1 is replaced by two half-coils 20a and 20b as illustrated. The beginning end of one coil and the opposite end of the other are connected to the two cords 54, and the two other ends are connected together to a commonmiddle lead 69; so that current will flow between cords 54 through the two coils in series in the same winding direction. When the two cords are connected across a circuit the'two half-coils together act like single coil 20. Middle lead extends up through head I! and one extension l9 to a contact plate 6! on the upper end of that extension. When the mounting core isplaced in the case, contact 6| engages a contact strip 62 which is secured to the under side of case head II. A binding post 62 mounted on head ll provides means for connecting a cord like cords 54. For smaller voltage rangesone uses the connection at 62, and the one of cords 54 which connects with the upper coil 200,. That cord may be distinctively colored for identification. Springs 40 and 21 may be, in this type of instrument, made weaker than in Fig. 1, or spring 21 may be merely located lower down. The pointer will then movefurther down in slot 45, for any given voltageapplied to the whole winding. The higher voltages, such as those indicated in Fig. 3, are applied to the half-winding and move the pointer over a calibrated scale such as that shown in Fig. 3. Voltages lower than those indicated are applied to thewhole winding and additional scale indications may be provided on the caseto indicate those voltages.

Although I have described my instrument as a potential indicator, although that istheuse for solenoid with a longitudinally movable armature core therein and a movable pointer, connected with the core; characterized by the provision of 2. An electrical measuring instrument of the type which comprises a slotted exterior case, a solenoidwith a longitudinally movable armature core therein and a movable ,pointer connected with the core; characterized by the provision of a unitary mounting core which comprises a coil spool with two end heads and a central longitu- ,dinal sleeve containing the movable core, and

laterally spaced longitudinal projections extending from one of said spool heads; the pointer beingmovably' supported on and between the ,two

longitudinal extensionsto move in a longitudinal plane; the case comprising a tubular side Wall and one end closure, and the unitary mounting core being removably arrangedin the case with one of the spool heads closing the other end of a unitary mounting core which comprises a coil spool with two end heads and a central longitudinal sleeve containing the movablecore, and

laterally spaced longitudinal projections extending from one of said spool heads; the pointer being movably supported on and between the two longitudinal extensions to move in a longitudinal plane; the case comprising a tubular side wall and one end closure, and the unitary mounting core being removablylarranged inthe case with one of the spool heads closing the other end of the case. s l l the case, with the mounting core projections extending to the vicinityof thecase head, and securing means for the mounting core projecting through the case head and extending into a mounting core projection.

,3. An electrical measuring instrument asspecified in claim 1; further characterized by the pointer mounting being in the form of a pivot shaft extending btweenthe two mounting core extensions on :a transvers axis.

G. MAHURIN. 

